Brief Summary of the Invention
The present invention relates to a device for contactless measuring of both width and thickness of an object moving along a straight path.
The invention could be used for measuring thickness and width of e.g. laterally conveyed wood and timber at an adjustment works.
For a long time, it has been desirable to have a compact solution for contactless measuring of both thickness and width simultaneously, and such that the measuring results could be passed further on to a PLS, a computer or a PC. Rotating objects or sensors touching the object to be measured have, in the long term, been found to cause larger or smaller inconveniences. Some pulse generators used for width measurements have been inclined to transmit pulses due to even small vibrations in the equipment to which the pulse generator is mounted, the measurements being activated by e.g. photoelectric cells. This problem is largest in those cases wherein a plank during measuring has been at rest in the area of measuring for some longer time. Another problem has been that the dull-edge on the wood/timber could contribute to erroneous measurements of both width and thickness. In an attempt to avoid erroneous measuring of the thickness, several values have been receipted by a computer. Subsequently, one uses the largest value.
This invention solves these problems by means of a single unit measuring both width and thickness touchlessly, and without any movable or rotating parts being included. Measuring both width and thickness takes place only at that moment the central line of the plank or object to be measured passes the centre of the measuring area of the camera. When the camera sees the front edge of the object to be measured, an internal search for the central line of the object to be measured starts. At the moment this is detected, the measuring is carried out. The measuring values are laid out in the order width, thickness 1 and thickness 2. The system initializes itself as soon as the object to be measured is out of the visual field of the camera.
The dull-edge problems illustrated in FIG. 4 are eliminated in that the CCD camera 11 in FIG. 5 used for the width measurement sees "around the corner" of the wood/timber piece 12 by means of a parabola-shaped mirror 1.
In order that the device is to function according to its intention, the width measurement, as shown in FIG. 1, requires camera 1, two parabola-shaped mirrors sp1 and sp2 as well as an elongated light source 2. For the thickness measurement, at least camera 2 and laser 1 are required. In those cases wherein one can not use a safe and sufficiently accurate lower edge reference, one has to use camera 3 and laser 2. For both thickness and width measurement, some electronics for converting the analog video signals to TTL levels is required, and further to digitize the values measured and lay these out to a communication gate, such that they can be fetched by a computer, PLS or PC.
From Norwegian patent NO 152,987 a system for measuring the diameter of logs is known, by means of light from a light source illuminating a parabolic mirror. From the mirror, the light is reflected toward the object to be measured. On the basis of the shadow portion of the object formed on a detector, the diameter is found. Use of parabolic mirrors and lights must be considered known on the basis of said patent. However, it is important to note that, in accordance with FIG. 3 of said patent specification, a power driven rotating plane mirror is used, and that one parabolic mirror only is used in order to carry out the measurement. When FIG. 4 of the patent specification shows two such mirrors, forming 90.degree. with each other in the longitudinal direction, this is because the measurement in the figure shown is carried out in two directions, and that these two measuring directions are turned 90.degree. in relation to each other.
The purpose of using parabola-shaped mirrors is, in addition to what has been mentioned in the preceding section, that objects having a given dimension, here width, shall not give differing measuring result when the distance to the object to be measured, or such as in this case, the thickness, varies.
Norwegian Patent No B 168,271 shows a device for optical measurement of elongated objects, such as sawn pieces of timber. The device comprises a camera, image processing devices and a mirror for reflecting the image of the object. According to the laying-out publication, the mirror may have different forms. However, it is not mentioned that the mirror necessarily has to be parabola-shaped and concave. It is obvious that the intention with the invention is to contract the image of an elongated object more in the longitudinal direction than in the lateral direction of the object, such that either the length only or both width and length of the object simultaneously are measurable by means of one and the same camera which scans the surface of the mirror.
The novel and particular feature of this invention as shown in FIG. 1 is in addition to measuring both width and thickness and carrying out the measurement at a defined moment when the central line of the object to be measured passes the centre of the measuring area, also that it--in order to measure the width--uses two parabola-shaped mirrors together with one CCD camera, in such a combination that one simultaneously avoids deviation of measuring values in that the object to be measured comes closer to the camera as well as avoids the use of a motor having plane mirrors or prisms which rotate. The camera which, in order to come away from the measuring zone of its own, looks obliquely into one of the mirrors, searches along a straight line in the longitudinal direction of the mirror. However, the camera will, based on the positioning thereof, in the mirror see a curved picture of an otherwise straight line. The consequence would be that the camera searching in a straight line, would sense only a small part of the image of the straight line. I.a., this is in order to counteract this unfortunate consequence that a mirror No. 2, which otherwise is quite equal to the first mirror, is mounted such that the concave sides of the two mirrors become turned 90.degree. relative to each other in the plane of the short sides (short dimensions). The fact that the angled positioning is in the plane of the short sides, is of substantial importance for this invention. A further and important feature is that the individual components may be mounted so close to each other that they may be assembled in a closed dust-tight cabinet having a narrow, elongated, transparent aperture only, thereby facilitating the cleaning.